Dielectric ceramic composition comprising lead-lanthanum titanate solid solution

ABSTRACT

Dielectric ceramic having a high dielectric constant and a low dielectric loss over a wide frequency range of 1 kHz to 30 MHz, a small temperature coefficient of dielectric constant, high stability with time, a high breakdown voltage and high mechanical strength is a sintered mixture composed essentially of 65 to 96 percent by weight of BaTiO3, 3 to 20 percent by weight of (Pb1 xLa2x(1 y)Ti1 xy xO3 xy)(where x is a 0.15 to 0.8 mole and y is 0.5 to 0.9 mole), 1 to 15 percent by weight of BaZrO3, and/or, as additives, up to 10 percent by weight of at least one additive selected from the group consisting of Bi2O3, Bi2(TiO3)3, Bi2(SnO5), Bi2(ZrO3) and SiO2.

mfi'fimfi 19] [1 l] Nitta et all. 1 May 0, 11973 [54] DIIELEC'HRM OERAMIC 3,440,067 4/1969 Fujiwara et al. ..106/39 R COMPOSHTION COMPRHSIING MEAD- LANTHANUM THTANATE SOLID SOLUTION [75] Inventors: Tsuneharu Nitta; Hiromitsu Tallti, both of Osaka; Kaneomi Nagase, Kyoto. all ofJapan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Kadoma, Osaka, Japan [22] Filed: Mar. 24, 1971 [211 Appl. No: 127,836

1 30 I Foreign Application Priority Data Apr. 2, 1970 Japan ..45/284l4 May 19, 1970 Japan. ..45/43182 June 9, 1970 Japan ..45/50068 [52] U.S. Cl ..1106/73.2,252/63.5,252/520 [51] lint. Cl. ..C04l1b 33/00 [58] lFielld 01f Search ..106/39 R; 252/635, 252/518, 528; 317/258 [56] References Cited UNITED STATES PATENTS 2,985,700 5/1961 Johnston.... ....106/39 R 3,268,783 8/1966 Saburi ....106/39 R 3,256,499 6/1966 Khouri et a1 ..252/520 3,292,062 12/1966 Gallagher ct al.. ....106/39 R 2,908,579 10/1959 Nelson et al ....lO6/39 R 2,289,211 7/1942 Ridgway ..106/39 R FOREIGN PATENTS OR APPLICATIONS 933,419 8/1963 Great Britain ..106/39 R OTHER PUBLICATIONS Saburi, O; Semiconducting Bodies in the Family of Barium Titanates; J. Amer. Chem. Soc., 44 (2) July 1961.pp. 54-63.

Gallagher, et al.; Preparation of Semiconducting Titanates; J. Amer. Chem. Soc., 46(8) August 1963. pp. 359365 Primary ExaminerL. Dewayne Rutledge Assistant ExaminerW. R. Satterfield Attorney-Wenderoth, Lind & Ponack 57 ABSTRACT Dielectric ceramic having a high dielectric constant and a low dielectric loss over a wide frequency range of 1 kHz to 30 MHz, a small temperature coefficient of dielectric constant, high stability with time, a high breakdown voltage and high mechanical strength is a sintered mixture composed essentially of 65 to 96 percent by weight of BaTiO;,, 3 to 20 percent by weight of [Pb, ,La. ,,,Ti, O ,,](where x is a 0.15 to 0.8 mole and y is 0.5 to 0.9 mole), l to 15 percent by weight of BaZr0 and/or, as additives, up to 10 percent by weight of at least one additive selected from the group consisting of Bi O Bi (TiO Bi (SnO Bi (ZrO and SiO 7 (Claims, No Drawings DIELECTRIC CERAMIC COOSITION COMPRISING LEAD-LANTIIANUM TITANATIE SOLID SOLUTION The present invention relates to novel ceramic materials which are used for capacitors, and more particularly to novel dielectric ceramic compositions comprising barium titanate, lead lanthanum titanate, barium zirconate, and/or, as additives, at least one additive selected from the group consisting of bismuth oxide, bismuth titanate, bismuth stannate, bismuth zirconate and silicon oxide.

The electronics industry requires a high dielectric material for making capacitors operating at high frequencies, for example, in a range of l to 30 MHZ. It is important in making such capacitors that the dielectric materials have a high dielectric constant and a low dielectric loss over a wide frequency range, a small temperature coefficient of dielectric constant, high stability with time, and a high breakdown voltage.

Although the conventional dielectric ceramics such as barium titanate are characterized by a high dielectric constant, they are not suitable for use in high frequency capacitors in the afore-indicated megahertz range because of having a large dielectric loss at frequencies above 1 MHz.

in order to meet present-day demands, the upper frequency limit should be higher than the conventional limit and preferrably at least 30 MHz, without disturbing and even improving the other desirable properties of ceramic dielectric materials.

Besides, modern electronics tends toward the miniaturization and molding of circuits, and for use in thin film capacitors, for example, it is desirable that dielectric materials have high mechanical strength.

Accordingly, a principal object of the present invention is to provide novel dielectric materials in the form of ceramics having a high dielectric constant and a low dielectric loss in a frequency range of at least up to 30 MHZ.

A further object of the present invention isto provide dielectric ceramics characterized by a high dielectric constant, a low dielectric loss, a small temperature coefficient of dielectric constant over a wide temperature interval, high stability with time, high breakdown voltage, and a high mechanical strength.

These and other objects of this invention will become apparent upon consideration of the following detailed description.

in accordance with the present invention, it has been discovered that a ceramic material of a fired combination composed essentially of 65 to 96 percent by weight of barium titanate (BaTiO 3 to 20 percent by weight of lead lanthanum titanate (Pb, ,La Ti O where x is 0.15 to 0.8 mole and barium to 0.9 mole), l to 15 percent by weight of barium zirconate (BaZrO and/or, as additives, up to percent by weight of at least one additive selected from the group consisting essentially of bismuth oxide (Bigog), bismuth titanate [Bi (T i 03%], bismuth stannate [Big SnO bismuth zirconate [Bi (ZrO and silicon oxide (SiO has a high dielectric constant and a low dielectric loss over a wide frequency range, a small temperature coefficient of dielectric constant, high stability with time, a high breakdown voltage, and high mechanical strength.

The component oxides are intimately mixed in the desired composition proportions and fired in accordance with a schedule set forth hereinafter for production of a fired ceramic body.

The raw materials for the ceramics are commercially pure grade barium titanate (BaTiO barium zirconate (BazrO and silicon oxide (SiO reagent grade lead oxide (PbO), titanium oxide (TiO and tin oxide ($110 and high purity zirconium oxide (ZrO bismuth oxide (Bi O and lanthanum oxide (La- 0 Any compound which is converted upon firing to the corresponding barium titanate, barium zirconate, lead oxide, titanium oxide, zirconium oxide, tin oxide, bismuth oxide, lanthanum oxide or silicon oxide can be used as a raw material. Batches of the raw materials are ball milled with a small amount of water for intimate mixing and then dried. Usually they are pressed loosely into a pellet form and calcined at a temperature of 750 to 950 C, for 2 hours in a covered platinum crucible. The calcined product is then powdered thoroughly and a few drops of distilled water are added to the powder. The powder is formed into discs. These discs are fired at a temperature ranging from 1,300 to 1,400 C for 2 hours, and then they are cooled at furnace power off.

Silver paste is fired on the disc surfaces to form electrodes in a per se conventional manner and then tested for dielectric properties.

The temperature coefficient of dielectric constant is obtained by measuring the capacitance over a range of temperature of 55 to +1 50 C and the variation is expressed by percentages in comparison with the value at 20 C.

A breakdown voltage test is performed in silicon oil at 100 C by applying a dc voltage.

A capacitance life test is carried out in a thermostat at C and more than 95 percent relative humidity for 1,000 hours and the variation in the value of capacitance is expressed by percentages.

Mechanical strength is measured in a per se conventional manner.

According to the present invention, it has been discovered that the following base compositions indicated in Table I can provide high dielectric constant materials having, particularly, a lower dielectric loss at frequencies of up to 30 MHz.

TABLE 1 Composition Preferable by weight BaTiO to 96 iq ani-m nx a-l- 3 to 20 BaZrO l to 15 In the formula shown in Table l, x has a value of from 0.15 to 0.8 mole and y has a value of from 0.5 to 0.9 mole.

The room temperature dielectric constant and dielectric loss over a range of l KHZ to 30 MHz of dielectric elements employing the ceramic materials in accordance with the present invention are shown as a function of compositions in Table II.

TABLE ll Dielectric property (at 20 C.)

Dielectric constant Dielectric loss (XIII- Pb ,La1, (l-y) 1 1 30 1 1 30 Ba'IiO; Tin o BaZrO; kHz. mHz. mHz. kHz. mHz. mile.

J: is 0.35 mole and 1 is 0.70 mole. "These samples are illustrations to indicate the poorer properties of dielectric ceramics which are outside the scope of the present invention.

Table 11 shows that the compositions within the range of Table I exhibit excellent dielectric properties. On the other hand, a dielectric material containing more than 96 percent by weight of BaTiO has a lower dielectric constant and a larger dielectric loss at high frequency. A decrease in the proportion of BaTiO below 65 percent by weight results in a dielectric material having a lower dielectric constant. An increase in the proportion of BaZrO above 15 percent by weight results in a sintered body having a larger dielectric loss. Variation by way of a decrease from 1 percent by weight of BaZrO results in a poorly sintered body. An increase in the proportion of Pb, ,La ,,,Ti O (where x is 0.15 to 0.8 mole and y is 0.5 to 0.9 mole) above percent by weight results in a dielectric material having an extremely low dielectric constant. A dielectric material containing less than 3 percent by weight of Pb, .I..a Ti, IOa I (where x is 0.15 to 0.8 mole and y is 0.5 to 0.9 mole) results in a very poorly sintered body.

it has been further discovered according to the present invention that said base compositions are preferably improved in the dielectric property, particularly a life characteristic of capacitance, by adding up to 10% by weight of at least one additive selected from the group consisting essentially of bismuth oxide (Bi O bismuth titanate [Bi (TiO bismuth stannate [Bi SnO and bismuth zirconate [Bi- (ZrO TABLE III Variation of x and y in Dielectric property (at 20 C.)

lb La (1 Tl x Dielectric constant Dielectric loss (X 10) 3xy e No. Value of x Value 01y 1 kHz, 1 mHz. 30 mliz. 1 kHz. 1 mHz. 30 mill.

0. 14 0. 51 865 1, 000 1, 640 m 320 580 0. 15 0. 50 2, 200 2,300 2, 330 100 107 110 0.33 0. 1, 240 1, 360 l, 520 260 335 450 0. 35 0. 70 3,050 3,100 3, 200 80 62 41 0. 39 0. 80 3, 000 3,100 3, 200 88 82 70 0. 52 0. 64 2, 730 2, 810 2, 980 85 80 65 0. 58 0. 2,150 2, 200 2, 300 124 132 140 0.58 0. 91 2, 430 2, 650 2, 820 160 200 500 0. 0. 90 2, 730 2, 810 2, 900 90 130 150 0. 57 0. 2, 580 2, 760 2, 810 103 96 U2 0. 71 0. 72 2, 440 2, 520 .2, 600 65 82 100 0. 0. 73 2, 100 2, 300 2, 350 68 105 0. 81 0. 73 1 470 1, 500 1, [310 1-10 %0 Each above composition is composed 0i80% hyweight oi BilTiOg, 12% by weight oiPb Lazi (+1-)') 11+xyx Oil-3y, and 8% by weight of BaZr0;, respectively.

"These samples are illustrations to indicate the poorer properties of dielectric ceramics which are outside the scope of the present inventio Turning now to a discussion of the Pb, ,,La .,,,Ti 0 component with which the present invention is particularly concerned, it has been found that Pb, La Ti O in which x has a value of 0.15 to 0.8 mole and y has a value of 0.5 to 0.9 mole, shows a single phase solid solution with a perovskitetype cubic symmetry. The fired combinations of P13 La2 T1 O3xy existing in such a single The ceramic specimens of these compositions show a slight change in a life test of capacitance with time, while the other dielectric properties still remain at a relatively high value. The room temperature dielectric constant and dielectric loss at a frequency of 30 MHz and the variation of capacitance with time of dielectric elements employing ceramic materials in accordance with the present invention are shown in Table IV.

TABLE 1V Additives (percent by wulght) Dielectric property Each above basiccomposition is composed of 80% by weight 0! IlnTiO 12% by weight l+Xy-x J-xy (where x is 0.35 mole and y is 7.0 111011) and 8% by weight The sample is an illustration to indicate the poorer properties of a dielectric. cl'rinnic which is outside the scope of the present invention.

Table IV shows that the composition in accordance with the present invention exhibits excellent stability with time.

Moreover, according to the present invention, it has been discovered that the addition of silicon oxide (SiO to said basic composition improves remarkably the mechanical strength. Good results are obtained by an addition of up to 10 percent by weight of silicon oxide (SiO to said basic composition. Table V shows the room temperature dielectric constant and dielectric loss at 30 MHz, and the mechanical strength of the dielectric ceramic materials according to this embodiment of the present invention.

TABLE V *Additives by weight) Property No. Dielectric Dielectric Mechanical constant at loss at C strength SiO, 20C, and and MHz 3OMH2 (X 10) (kg/cm) 16 3200 41 l 140 36 0.5 3230 56 1450 37 1.0 3000 42 1820 38 5.0 2810 41 2250 39 10.0 2540 42 2460 40" l 1.0 1540 42 2580 Each above basic composition is composed of 80% by weight of BaTiO 12% by weight of Pb La JL O Awhere x is 0.35 mole and y is 0.70 mole), and 8% by weight of BaZrO respectively.

** The sample is an illustration to indicate the poorer properties of a dielectric ceramic which is outside the scope of the present invention.

The composition within the range of the present invention shows a higher mechanical strength and a relative- 1y high dielectric property.

Another important property contributing to the usefulness of the dielectric materials according to the present invention is that the temperature coefficient of dielectric constant is small over a wide temperature range and the breakdown voltage is high at a high temperature.

Table V1 shows the temperature coefficient of dielectric constant and the breakdown voltage at 100 C for ceramic materials in accordance with the present invention.

TABLE V1 Property Temperature coefi'lcient of dielectric constant (-C to +15C) Breakdown voltage at -55C +150C 100C (kvlmm) 4 10 +3.3 36.6 1 l +2.1 2 29.6 16 -1.0 1.5 27.5 29 3.2 +3.0 31.1 32 -l.4 0.9 32.0 34 l .6 -l .2 30.0 35 -2.0 1'0 35.8 38 -0.8 -l.4 37.5

As seen in Table V1, the temperature coefficient of dielectric constant of the compositions in accordance with the present invention are very small over the wide temperature range of 55 to +150 C and the breakdown voltage is more than 20 ltV/mm at a relatively high temperature of 100 C.

The dielectric compositions according to the present invention can be used for making dielectric capacitors for wide frequency use, for example, coupling or bypass capacitors.

What is claimed is:

11. A dielectric ceramic composition comprising a sintered mixture consisting essentially of, to 96 percent by weight of BaTiO 3 to 20 percent by weight of Pb 1221 5 Ti 0 i solid solution in perovshite form wherein x has a value of from 0.15 to 0.8 mole and y has a value of from 0.5 to 0.9 mole and l to 15 percent by weight of BaZrOQ.

2. A dielectric ceramic composition according to claim 11, wherein said sintered mixture further includes up to 10 percent by weight of at least one additive selected from the group consisting of Bi O Bi (TiO Bigsnog, and

3. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially Eli- 0 d. A dielectric ceramic composition according claim 2 wherein said additive consists essentially Bi (TiO 5. A dielectric ceramic composition according claim 2 wherein said additive consists essentially Bi SnO 6. A dielectric ceramic composition according claim Z wherein said additive consists essentially 2( a)s- 7. A dielectric ceramic composition according claim 2 whereinsaid additive consists essentially S102. 

2. A dielectric ceramic composition according to claim 1, wherein said sintered mixture further includes up to 10 percent by weight of at least one additive selected from the group consisting of Bi2O3, Bi2(TiO3)3, Bi2SnO5, Bi2(ZrO3)3 and SiO2.
 3. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially of Bi2O3.
 4. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially of Bi2(TiO3)3.
 5. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially of Bi2SnO5.
 6. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially of Bi2(ZrO3)3.
 7. A dielectric ceramic composition according to claim 2 wherein said additive consists essentially of SiO2. 